Our long-term objective is to expand the basic understanding of vestibular reflexes by conducting experiments that will help clarify the anatomy and physiology of a particular evoked response. In the present application there are three specific aims. The first aim is to determine the optimal parameters for eliciting a novel auditory evoked potential measured from the triceps muscle called the triceps auditory evoked myogenic potential (TAEMP). The second aim is to study the TAEMP in patients with specific otoneurological pathologies to determine how the TAEMP resembles and differs from the conventional sternocleidomastoid vestibular evoked myogenic potential (SVEMP). The third specific aim is to compare the TAEMP and the SVEMP in cervical spinal cord lesions. The research design is as follows. For the first aim, we will employ methodology similar to that of Akin and Murnane (2001), used to characterize the (SVEMP) in the neck. In 16 normal subjects we will determine the sensitivity of the TAEMP to stimulus intensity, frequency, and muscle contraction, and head turning parameters. This will establish the optimal method for eliciting the response. For the second aim we will examine the TAEMP in 12 patients with specific isolated unilateral vestibular and auditory conditions (sensorineural hearing loss, vestibular loss due to surgical section). We hypothesize that the TAEMP will resemble the SVEMP in that it will be present in spite of unilateral hearing loss and absent in patients with unilateral vestibular loss. For the third aim we will compare the TAEMP and SVEMP in subjects with spinal cord lesions at C5-C7. We hypothesize that the SVEMP will be preserved, while the TAEMP will be attenuated or absent. The rationale for characterizing the TAEMP is that a better understanding of this novel acoustically evoked potential, that traverses the cervical spinal cord, will provide information complementary to that of the conventional SVEMP, and may translate into methods for evaluating patients with symptoms of dizziness and imbalance. The technique will be: (1) vary four parameters (force exerted by triceps; acoustic stimulus intensity; acoustic stimulus frequency; head position straight ahead or turned 90 degrees towards the outstretched arm) to determine the optimal combination for the TAEMP in normal subjects; (2) compare the TAEMP (which may be vestibular or auditory or both) with the SVEMP (known to be vestibular) in subjects with specific pathologies (vestibular nerve section, sensorineural deafness) using the optimal parameters from part 1 to identify specific similarities and differences between the SVEMP and the TAEMP. Lay language: We propose to characterize a novel evoked potential in the arm muscles elicited by loud sounds. These experiments will establish the best way to obtain this response as well as clarify its similarities to and differences from a more conventional test. The results will clarify the anatomy and physiology of the neural pathways involved in this response, and may eventually be translated into improved techniques for diagnosing and treating patients suffering from dizziness and balance disorders. [unreadable] [unreadable] [unreadable] [unreadable]